Generally, a utilization of a noble metal as an electrode material for an electrochemical sensor can achieve a high stability and a high reproducibility of detection and is ready a well-known technique in the field of electrochemistry. But, in the sensor, the only demand of the noble metal is a surface of an electrode, and other surfaces of the noble metal are unnecessary. Especially, for a disposable strip, the noble metal surfaces rather than the electrode are all squanders. The main purpose of the present invention is to provide a structure and a manufacturing method of a low-price metal electrode in a disposable electrochemical sensor strip for significantly reducing the demand of the noble metal and further reducing the cost.
The metal electrode according to the present invention also can be applied in various metal-catalyzed electrodes (not only noble metals) with a direct catalysis, besides in a noble electrode without chemical interference. The disposable electrode and the sensor according to the present invention can be suitable for all kinds of electrochemical detection electrodes, biosensors, fluid biochemical sensor (e.g., sewage, insecticide concentration, and heavy metal sensor strips), domestic medical application (e.g., blood glucose, uric acid, and cholesterol sensor strip).
The principle of electrochemical sensor has been developed and applied in detecting all kinds of fluid biochemical ingredient. An electrochemical sensor may have different configurations for conforming to different functions. Please refer to FIG. 1. FIG. 1 shows that a basic framework of an electrochemical detecting device 10 includes the following components:
1. A container 12 for containing a fluid sample to be an electrochemical measure region 13.
2. A chemical reagent 14 for chemically reacting with an analyte contained in the fluid sample 11 and generating an output signal with an electric parameter, wherein the electric parameter is corresponding to a biochemical ingredient of the analyte contained in the fluid sample 11. For example, if the fluid sample 11 is human blood and the analyte is glucose, the chemical reagent 14 is basically a glucose oxidase and a complex thereof.
3. Plural testing electrodes, as shown in FIG. 1, a counter electrode 15, a working electrode 16, and a reference electrode 17, for transmitting a working voltage for an electrochemical reaction from an electrochemical meter 18 to the container 12 and again transmitting the electric parameter to the electrochemical meter 18 after the analyte contained in the fluid sample 11 undergoes an electrochemical reaction so that the electrochemical meter 18 can process a numerical analysis and then display the result thereon.
4. An electrochemical meter 18 for providing the working voltage (or current) needed by the electrochemical reaction and measuring the electric parameter (output voltage or current) produced by the electrochemical reaction to record, process the numerical analysis and display the testing data.
Meanwhile, plural testing electrodes can only include the counter electrode and the working electrode or further include a reference electrode. Moreover, a detecting electrode could be included as a fourth electrode. The number of the plural testing electrodes is varied according to the requirement of the electrochemical reaction.
The electrodes of different functions are made of different materials. In the laboratory, the counter electrode 15 is made of any conductive material, however the lower the conductive resistance the better the effect, such as a copper, a silver, a nickel, a graphite, a carbon, a gold, a platinum or other conductive materials, or can be a conductive membrane electrode formed by printing a carbon paste or a silver paste. The most common structure of the reference electrode 17 is a modified electrode 171 produced by means of printing or electroplating an Ag/AgCl film. Because the electric potential of the Ag/AgCl film is quite stable, it is extensively used as the reference electrode.
The selection of the working electrode 16 is more complex and can be sorted as two types, one is an electron-transfer mediator modified working electrode and the other is a metal-catalyzed electrode. The electron-transfer mediator modified working electrode has a chemical reagent immobilized thereon, wherein the chemical reagent includes an enzyme (such as a glucose oxidase) and a redox mediator (such as a potassium ferricyanide which is extensively used in the glucose testing piece). The enzyme and the analyte will react with each other to produce a new chemical compound (such as H2O2), the electrons generated from the redox reaction between the mediator and H2O2 is utilized to produce an electric signal, and through the electrode, the electric parameter can be output. The main purpose of this kind of electrode is only simply a conductor and is not involved in chemical catalysis. However, the material of the electrode should be selected specifically to avoid a chemical reaction with the fluid sample 11 or the chemical reagent 14 thereby interfering with the result.
The electrode without the chemical interference should be made of an inert conductive material, which is generally a noble metal (such as a gold, a platinum, a palladium, or a rhodium), or a carbon containing material (such as a carbon base screen printing electrode or a graphite bar). Furthermore, because carbon and the noble metal have no chemical reactivity in a low temperature, the chemical interference would not happen. However, because the noble metal is more expensive, the carbon made electrode is usually applied as the electron-transfer mediator modified working electrode.
As to the metal-catalyzed electrode, it is made of a material which will directly electrochemically react with the chemical reagent, the analyte, or the derivatives thereof, and has an ability of direct catalysis or a function of a single selectivity for the analyte. Thus, the mediator is not needed to add into the chemical reagent. This kind of electrode, not only needs to be made of a chemically inactive metal, but also is generally made of a material that must have an ability to catalyze the reaction. Therefore, the material thereof should not be limited to be a noble metal but matched with the analyte, such as a copper, a titanium, a nickel, a gold, a platinum, a palladium, or a rhodium . . . etc., (for example, a rhodium electrode has an excellent ability to directly catalyze H2O2).
The two types of metal electrodes described above both have a high cost of the material and the processes when being formed under a conventional manufacturing method, especially the noble metal. Consequently, although the noble metal has a better stability, it still cannot be the mainstream of the disposable medical treatment testing in family. Nowadays, the biggest requirement of the biosensor is the medical treatment in family for a blood glucose, a uric acid or a cholesterol . . . etc. And, the electrode used by these biosensors mostly belongs to the electron-transfer mediator modified working electrode, and thus the disposable testing sheet of the biosensor can has the carbon base screen printing electrode printed thereon for reducing the cost, as described in U.S. Pat. No. 5,985,116, which is a typical example.
Please refer to FIG. 2 which shows the example described in U.S. Pat. No. 5,997,817. In this patent, two conductive metal tracks 201 and 202 both coated by a palladium are fixed on an insulative backing 203 with an identical size for being the metal electrode of the sensor. A working electrode 204 and a counter electrode 205, electrode leads 206 and 207, and signal output terminals 208 and 209 are all integrally formed by palladium. However, the positions that must be formed by palladium are only two tiny sections of the working electrode 204 and the counter electrode 205, and the other portions can only be formed by materials having a conductive characteristic rather than noble metal-palladium.
Further refer to FIG. 3 in which shows the example described in EP 1 098 000 and is another manufacturing method for the metal electrode. In this patent, an insulation sheet 301 previously injection molded has positions of a pattern 302 surrounded by recesses and islands 306, an electrode lead 303, and output terminals 304 and 305. Then, metallic deposit proceeds to deposit a metal layer on the surface of plastic insulation sheet. Due to all the surface of the insulation sheet being covered by deposited metal, an additional process has to be proceeded for removal of metal layer on the islands and remaining the patterns, the electrode leads and the output terminals. Thus, this method has a high cost and is only suitable for the electrode only formed by one kind of metal.
According to the technical defects described above, for reducing the manufacturing cost of the metal electrode in the disposable sensor strip and overcoming the problem of wasting the noble metal, the applicant devoted himself to develop a “structure and manufacturing method of disposable electrochemical sensor strip” through a series of experiments, tests and researches. In addition to effectively solve the wasting problem of the noble metal in prior arts, the electrodes according to the present invention can be formed or modified in advance respectively in different electroplating containers in a great quantity, and then be assembled to an insulation sheet for reducing manufacturing time thereof.
Furthermore, in addition to be employed as the noble metal electrode requiring no chemical interference, the metal electrode according to the present invention can also be employed as the metal-catalyzed electrode which has a direct catalyzing function. And, the disposable electrode and the sensor according to the present invention can be applied to all kinds of electrochemical testing electrodes, biosensors, biochemical analyte sensors for fluid (e.g., testing strips for a sewage, a pesticide content, a heavy metal ingredient etc.), all kinds of domestically medical treatment testing strips (e.g., testing strips for a blood glucose, a uric acid, and a cholesterol).